1. Field of the Invention
This invention relates to producing metal phosphorus trisulfides. More particularly, this invention relates to producing metal phosphorus trisulfide by reacting metal phosphides with phosphorus sulfides. Still more particularly, this invention is a process for producing relatively pure metal phosphorus trisulfides of the formula MPS.sub.3 wherein M is a metal selected from the group consisting of Mg, Ca, Sr, V, Mn, Fe, Co, Ni, Pd, Zn, Cd, Hg, Sn, Pb, Sm, Eu, Yb and mixtures thereof, wherein phosphides of said metals are reacted with phosphorus trisulfides in a reaction zone at relatively mild reaction conditions, including a temperature ranging from about 300.degree.-600.degree. C. and wherein said phosphorus sulfides are present in the reaction zone at least in the liquid form and in an amount sufficient to exceed the amount of P and S stoichiometrically required to form the desired MPS.sub.3.
2. Description of the Prior Art
Metal phosphorus trisulfides of the general formula MPS.sub.3 are known in the art. In 1899 Ferrand (M. L. Ferrand Concerning Some Metallic Sulfophosphides, Ann. Chim. Phys., 17, 388-432 (1899).) prepared small quantities of phosphorus trisulfides of iron, nickel, zinc and lead by heating the metals or their sulfides with elemental phosphorus and sulfur or in the presence of phosphorus pentasulfide vapors to a cherry red heat (i.e., 700.degree.-800.degree. C.), but was unable to prepare the metal phosphorus trisulfides of manganese and cobalt. In all cases, the quantity of metal phosphorus trisulfides produced was extremely small, comprising small crystals often intimately mixed with other reaction products. As Ferrand noted, the production of side products along with the desired MPS.sub.3 occurs almost invariably. These side products usually have chemical and physical properties very similar to those of the desired MPS.sub.3 rendering separation of the side products from the MPS.sub.3 virtually impossible or at least impractical. Thompson et al (U.S. Pat. No. 4,049,879) disclose the preparation of small quantities of iron, nickel and manganese phosphorus trisulfides by heating stoichiometric amounts of the elements, along with iodine, for at least 6 days at a temperature of about 700.degree. C. As was the case with Ferrand, extremely small quantities (i.e., .ltoreq.1 gram) of the metal phosphorus trisulfides were produced.
Hence, because of the potential importance and usefulness of metal phosphorus trisulfides as lubricants and electrode-active materials for batteries, there is a need for a method or process of producing these materials in larger quantities at reasonable reaction rates and under conditions and with starting materials such that any reaction products formed other than the desired MPS.sub.3 are readily separated therefrom. These criteria are achieved with the process of the present invention.